Trying to decompress uncompressed output with Busybox gunzip will fail even with
the -cf flag passed. 

Steps to Reproduce
------------------

    echo "uncompressed content" >> file
    gunzip -cf file

Actual Results
--------------

    gunzip: invalid magic

Expected Results
----------------

    uncompressed content

This expected behavior is given by the man page for GNU gunzip:

> -f --force: If the input data is not in a format recognized by gzip, and
> if the option --stdout is also given, copy the input data without change to
> the standard output: let zcat behave as cat.

Build date & Hardware
---------------------

Unknown: I first encountered this in the biocontainers Docker images, and created the above example with the busybox:1.34.1-uclibc Docker image.